Alkaliphiles are defined as organisms which exhibit optimum growth in an alkaline pH environment, particularly in excess of pH 8, and generally in the range between pH 9 and 10. Alkaliphiles may also be found living in environments having a pH as high as 12. Obligate alkaliphiles are incapable of growth at neutral pH.
Alkaliphiles may be found in such everyday environments as garden soil, presumably due to transient alkaline conditions caused by biological activity such as ammonification, sulphate reduction or photosynthesis. A much richer source of a greater variety of alkaliphilic organisms may be found in naturally occurring, stable alkaline environments such as soda lakes.
A more detailed study of soda lakes and alkaliphilic organisms in general is provided in Grant, W. D., Mwatha, W. E. and Jones, B. E. ((1990) FEMS Microbiology Reviews, 75, 255-270), the text of which is hereby incorporated by reference. Lists of alkaline soda lakes may be found in the publications of Grant, W. D. and Tindall, B. J. in Microbes in Extreme Environments, (eds. R. A. Herbert and G. A. Codd); Academic Press, London, (1986), pp. 22-54; and Tindall, B. J. in Halophilic Bacteria, Volume 1, (ed. F. Rodriguez-Valera); CRC Press Inc., Boca Raton, Fla., (1988), pp. 31-70, both texts are also hereby incorporated by reference.
Alkaliphiles, the majority of which are Bacillus species, have been isolated from non-saline environments and are discussed by Horikoshi, K. and Akiba, T. in Alkalophilic Microorganisms (Springer-Verlag, Berlin, Heidelberg, N.Y., (1982)). However, alkaliphilic organisms from saline and alkaline environments such as lakes are not discussed therein. Strictly anaerobic bacteria from alkaline, hypersaline, environments have been recently described by Shiba, H. in Superbugs (eds. K. Horikoshi and W. D. Grant); Japan Scientific Societies Press, Tokyo and Springer-Verlag, Berlin, Heidelberg, N.Y., (1991), pp. 191-211; and by Nakatsugawa. N., ibid, pp. 212-220.
Soda lakes, which may be found in various locations around the world, are caused by a combination of geological, geographical and climatic conditions. They are characterized by the presence of large amounts of sodium carbonate (or complexes thereof) formed by evaporative concentration, as well as by the corresponding lack of Ca.sup.2+ and Mg.sup.2+ which would remove carbonate ions as insoluble salts. Other salts such as NaCl may also concentrate resulting in environments which are both alkaline and saline.
Despite this apparently harsh environment, soda lakes are nevertheless home to a large population of prokaryotes, a few types of which may dominate as permanent or seasonal blooms. The organisms range from alkaliphilic cyanobacteria to haloalkaliphilic archaeobacteria. Moreover, it is not unusual to find common types of alkaliphilic organisms inhabiting soda lakes in various widely dispersed locations throughout the world such as in the East African Rift Valley, in the western U.S., Tibet, China and Hungary. For example, natronobacteria have been isolated and identified in soda lakes located in China (Wang, D. and Tang, Q., "Natronobacterium from Soda Lakes of China" in Recent Advances in Microbial Ecology (Proceedings of the 5th International Symposium on Microbial Ecology, eds. T. Hattori et al.); Japan Scientific Societies Press, Tokyo, (1989), pp. 68-72) and in the western U.S. (Morth, S. and Tindall, B. J. (1985) System. Appl. Microbiol., 6, 247-250). Natronobacteria have also been found in soda lakes located in Tibet (W. D. Grant, unpublished observations) and India (Upasani, V. and Desai, S. (1990) Arch. Microbiol., 154, pp. 589-593 ).
Alkaliphiles have already made an impact in the application of biotechnology for the manufacture of consumer products. Alkali-tolerant enzymes produced by alkaliphilic microorganisms have already found use in industrial processes and have considerable economic potential. For example, these enzymes are currently used in detergent compositions and in leather tanning, and are foreseen to find applications in the food, waste treatment and textile industries. Additionally, alkaliphiles and their enzymes are potentially useful for biotransformations, especially in the synthesis of pure enantiomers.